Hi Zhangjin, hi Yuan,
On Fri, Jul 28, 2023 at 11:50:31PM +0800, Zhangjin Wu wrote:
Hi, Yuan
pipe is crucial for shell.
As the syscall manpage[1] shows, pipe() is just one of the exceptions how may require two return registers in some platforms, e.g.: arch/mips/kernel/syscall.c
* For historic reasons the pipe(2) syscall on MIPS has an unusual calling * convention. It returns results in registers $v0 / $v1 which means there * is no need for it to do verify the validity of a userspace pointer * argument. Historically that used to be expensive in Linux. These days * the performance advantage is negligible. */(...)
Ah indeed! I vaguely remembered that I had left that one aside for some time but did not remember why. Now I remember that I couldn't handle the MIPS implementation by then while it used to be my primary target.
Seems pipe() is the **only** one some architectures (except Alpha) return two values, and now we have pipe2(), so, it is ok for us to simply use pipe2() instead ;-)
Since we are able to use pipe2() for pipe() (introduced from early Linux 2.6.27, glibc 2.9) and use getpid+getppid for getxpid, getuid+geteuid for getxuid and getgid+getegit for getxgid.
So, it is possible provide such pipe() as a wraper of pipe2() and
Indeed.
getxpid, getxuid and getxgid as wrappers of their corresponding syscall pairs,
I doubt anyone needs these ones, I didn't know them and do not even have their man page. Let's keep the focus on what developers really use.
Yeah.
then, no need to provide a second return value for all of the existing architectures, for example:
#ifndef pipe int pipe(int pipefd[2]) { pipe2(pipefd, 0); } #endifAnd for mips:
// may be in tools/include/nolibc/types.h ? struct fd_pair { long fd[2]; }; // tools/include/nolibc/arch-mips.h struct fd_pair pipe(void) {
[...]
pipe2(pipefds, 0);
[...]
}This one does not have the correct prototype for the function exposed to the user, pipe really is "int pipe(int pipefd[2])". Maybe you were thinking about sys_pipe() instead ? But since MIPS also has pipe2() now, there's no reason to make an exception.
Yes, pipe2() should be a better choice, but I have seen this sentence in syscall manpage [1]:
/* On Alpha, IA-64, MIPS, SuperH, and SPARC/SPARC64, pipe() has the following prototype; see NOTES */
#include <unistd.h>
struct fd_pair { long fd[2]; }; struct fd_pair pipe(void);
If it is about syscall, then we are ok to align all of the architectures together to use "int pipe(int pipefd[2])", otherwise, it will be required to define them in their own arch-<ARCH>.h, just like some defined for arch-s390.h.
[1]: https://www.man7.org/linux/man-pages/man2/pipe.2.html
To use such method, the test case should be changed too, perhaps an easier method is even only provide pipe2() for all and let users define their own pipe() if really required, we also need to change the test case.
No, we need to provide users with what they need to compile standard code. If we rely on pipe2() to deliver pipe(), that's fine. We can even do it per-arch if there are constraints but it seems to me that pipe2() is OK.
Ok.
Thanks, Zhangjin
Thanks, Willy